An organic electroluminescent device is a light emitting device using a phenomenon in which emission of light is generated by excitons formed by recombination of electrons and holes injected into an organic substance. In recent years, development of a display using the organic electroluminescent device increases. This is because the organic electroluminescent device can provide a wider viewing angle, faster response speed, and higher contrast than does a liquid crystal display.
In general, the organic electroluminescent device has a structure in which an organic layer is sandwiched between a cathode and an anode. When a voltage is applied to the organic electroluminescent device, an electron is injected as a carrier from the cathode, and a hole is injected as a carrier from the anode. When the carriers recombine together in the organic layer, an exciton is formed, thereby emitting light.
Generally, the organic electroluminescent device includes: an organic layer including a light emitting layer, a hole transporting layer, an electron transporting layer, etc.; and a pair of electrodes (a cathode and an anode) which opposes each other through the organic layer. Usually, the organic layer usually has a very small thickness, for example, in the order of 100 nm. Therefore, a leakage failure between electrodes or a failure in dielectric strength between electrodes may occur due to contamination by fine foreign matters, extraneous on the organic layer, etc.
If such a failure occurs, a black dot, a dark line, or a black line may be observed when the organic electroluminescent device is activated, thereby deteriorating a display quality of the organic luminescent device. Even when a black dot, or the like, does not occur, a leakage current may occur in an area with an insufficient dielectric strength, during activation of the organic electroluminescent device. In particular, the size of the organic electroluminescent device recently increases, and a probability of such failures tends to increase, which is a great problem.
In light of such circumstances, there is a known method for restoring an insufficient insulation area between a pair of electrodes in an organic electroluminescent device including a plurality of types of organic layers which include a plurality of light emitting layers that emit different colors of light, and a pair of electrodes opposing each other through the plurality of types of organic layers. According to the method, a reverse bias voltage is applied to the plurality of types of organic layers under application conditions which vary by color of light emission, whereby isolating the insufficient insulation area between the pair of electrodes. Accordingly, the insufficient insulation area is restored (see, for example, Patent Document 1).
There is another known method for manufacturing an organic electroluminescent element including a layered body formed by sequentially stacking, on a substrate, an anode, an organic layer including a light emitting layer, and a cathode. The method includes: a process of forming the cathode by sequentially laying a first conductive layer, a buffer layer, and a second conductive layer; and a process of subjecting the formed layered body to aging.
In the method, the cathode is formed by sequentially stacking the first conductive layer, the buffer layer, and the second conductive layer. Further, after formation of the layered body, the body is subjected to aging. Accordingly, it is possible to manufacture an organic electronic luminescent element that requires a drive voltage which is lower than that of the related-art organic electroluminescent element (see, for example, Patent Document 2).
There is a proposed lighting apparatus including direct current power supply means for supplying a desired direct current voltage to an organic electroluminescent element; detection means for detecting shutoff of the voltage supplied from the direct current power supply means; and reverse voltage supply means for supplying a voltage of a reverse characteristic to the organic electroluminescent element when the voltage supplied from the direct current power supply means is shut off (Patent Document 3).    Patent Document 1: JP-A-2007-207703    Patent Document 2: JP-A-2007-200662    Patent Document 3: JP-A-2007-149463